This invention relates to silver coating of materials.
One particular device in which a silver coating is especially advantageous is the ceramic filter. Such filters typically include a block of ceramic material with a line of parallel holes and a conductive coating formed over most of the block including the interior portions of the holes. The coated holes function as resonator rods in coupling a selected microwave signal from the input to the output of the filter (see, e.g., U.S. Pat. No. 4,523,162 issued to Johnson, which is incorporated by reference herein).
In such devices, the conductive coating on the surface of the ceramic is preferably silver. However, applying the silver coating can be difficult and expensive in view of the presence of the holes in the ceramic. A typical operation involves painting silver paste on the surface of the ceramic. This usually requires at least two coats and special attention to pushing the paste into the holes. An alternative method of fabrication involves sensitizing the surface with an electroless copper layer, electroplating a thin layer of copper thereon, and then electroplating silver thereover. While adequate, such a conductive coating usually does not provide as good a coupling efficiency as a solid silver coating.
It is, therefore, an object of the invention to provide a relatively inexpensive method for providing silver coatings on ceramic material.